Potencial energético dos resíduos de desbastes em plantações de Pinus taeda no estado do Paraná, Brasil

Abstract

The objectives of this research were: i) to evaluate the weight of the residues left on the soil after thinníng operations; ii) to determine the heat content of the residue components; and iii) to estimate the energy potential, per unit of area, of the residual biomass. The data were collected from 7, 10, and 14 years old stands of Pinus taeda (loblolly pine), that would be submitted to the 1st, 2nd, and 3rd thinnings, respectively. The plantations are owned by ”Indústrias Klabin de Papel e Celulose” and are located in Telêmaco Borba county, State of Paraná, Southern Brazil. In order to obtain the equations for estimating the residues weight, 51 trees from the 7 years old stand, 39 from the 10 years old, and 25 from the 14 years old were sampled. These trees were deIimbed and stripped, and the residual material classified into the following classes: needles, small branches (less than 0.7 cm diameter), medium branches (0.7 to 2.5 cm diameter), and large branches (2.5 to 7.0 cm diameter). Branches and tops over 7.0 cm diameter were not included because they are harvested for commercial use. The following informations were recorded from the sampled trees: diameter (DBH), total height, and commercial height. These parameters comprised the independent variables used to generate the equations for estimating the weight of the crown components. Randon samples from needles and different sizes of branches were collected and taken to the laboratory for determining the dry weights and, afterwards, the heat content. Results showed that the DBH was the most efficient independent variable for estimating the dry weight of the crown components through mathematical models. Except the large branches that were better estimated by second degree equations of the type Y = a + b DBH + c DBH2 , all other crown components were estimated with higher precision through Iogarithmic equations of the type In Y = a + b In DBH. Total dry weight of residual biomass calculated through general equations was 8.266 ton/ha, 14.972 ton/ha, and 14.000 ton/ha in the frist, second and third thinnings, respectively. The average heat content used in the Cªlculations was 19.24 MJ/kg for total crown residues, and 19.11 MJ/kg for crown without needles. The energy production potential of the total residual biomass, for oven dried material, was 3.9 tons of oil equivalent lTOE) per hectare in the 1th thinning, 7.1 TOE/ha in the 2nd, and 6.6 TOE/ha in the 3“. Considering only the woody residues, i.e., excluding the needles, the energy potential for oven dried material dropped to 3.0 TOE/ha, 5.3 TOE/ha, and 5.0 TOE/ha, respectively. Moisture contents of 40, 80, and 120% (dry weight basis) reduce the energy potential to, respectively, 94, 89, and 83% of the values estimated for oven dried material.